Joined
·
3,604 Posts
imported post
I have noticed this topic coming up quite frequently. A search would reveal a lot of different threads and I actually started one a while back myself but I wanted to add a more recent one to help others with this....
This method is works only if there is a schrader/air valve in the top fork bolt.
I have started doing the fork oil change as annual maintenance. There is a method to do it where you can do it very simply and get the level right everytime.
The confusing thing is that level and volume keeps getting interchanged but in essence, they are basically one and the same. If you can figure out the level (distance from the top of the fork tube), then you will already know the volume (amount of cc's) that need to be added. These forks need the level to be equal in both forks even though different amounts of oil go in each. This is because there are different components in the left as opposed to the right and this changes the amounts of oil each one holds. (Although this doesn't apply to Interstate models, they use equal volume in both forks.) But the one constant is that the level will end up being identical. This is because of the level of air needs to be the same in both sides. Even though Progressive says to add no air which technically is correct, there is still air in the forks and this plays into the damping. When the forks are compressed, as in driving down the street, going over bumps, cornering, etc... This amount of air will also play into the mechanics of how the fork works. Because of this, the amount of air needs to be identical in each or there will be different amounts of pressures at work on the left and right forks which could cause a serious handling issue.
An example of volume and level.... Let say you need 1-1/2 cup of milk. You pull out a glass measuring cup and carefully measure it out using the markings. Now you pour that into another glass cup that you plan on using all the time that has no markings. So after you pour the milk into this separate glass, you make a mark at the level where the milk is. The next time you need 1-1/2 cups of milk, you will no longer need to measure it, you just pour the milk into this glass up to the mark and if it goes over, you pour out the excess. If it's too low, just add some more. This will work for everytime you need 1-1/2 cups of milk. Technically you are still measuring out 1-1/2 cups each time but you already know in advance that putting the milk to the mark will get you the amount you need. So no need to think about it.
Satan on this board took the time to do some extensive measuring of the 88-94 and 95-00 forks and simplified the levels. Most times the service manual only gives the levels and volume with springs out and the forks fully collapsed. That is the hard way. Changing the fork oil with the forks fully extended with the springs still in wasn't known and most folks took their best guess at what it should be. But this information is what was wanted. He was in the middle of a fork rebuild so was able to take both measurements and this is what he came up with:
Oil fill with forks collapsed and springs out (from the shop manuals):
239mm / 9.4" for 88-94
194mm / 7.6" for 95-up
Of course that kinda sucks if you've got springs in your bike and you're refilling through the air valve...
... so measuring from the TOP OF THE FORK NUT (schrader valve removed) looks more like this --
Oil fill with forks fully extended and springs installed (measured from the top-plane of the fork nut with the air valve removed):
400mm / 15.75" for 88-94 (Progressive springs installed tight end down)
406mm / ~16" for 88-94 (Progressive springs installed loose end down)
408mm / ~16.1" for 88-94 (OEM springs installed)
* 355mm / ~14" for '95+ (Progressive springs installed tight end down)
* 361mm / ~14.2" for '95+ (Progressive springs installed loose end down)
* 363mm / ~14.3" for '95+ (OEM springs installed)
With that said, the method is foolproof and actually pretty easy way to do it quickly and get the same results each time. All you need is a way to jack up the front of the bike while on center stand so the forks are fully extended, a bottle of your favorite fork oil, a length of aquarium air hose and a syringe like this one:
![]()
(Satan used a length IIRC of 3/8" copper tubing straightened and a fender washer to set his level. I use the aquarium tubing because I already had it.) Cut 2 lengths of aquarium tubing. The first one make long enough to reach the bottom of the bottle of fork oil and attach this one first. Second, based on above mentioned levels, figure out which measurement fits your particular application and cut the aquarium tubing to the proper length. If the tubing is too tight, you can use a larger phillips head screwdriver to expand the tubing. It usually has quite a bit of flex before it tears. Obviously drain the old fluid during which removing the schrader/air valve makes it drain quicker. I will sometimes usea nozzleon my compressor set at lowand stick it in the top holeand help blow some of the remaining fluid out. Don't use too high a pressure or fluid will spray everywhere out the drain hole and make a mess. After it finishes draining, put the drain plug back in andstart pulling fork fluid from the bottle through the first aquarium tubing filling the syringe. Now take the end of the aquarium tubing and start putting it through the hole left by the removed schrader valve. Squeeze out the new fluid. Do this about 5 times in each side (based on using a 60cc syringe). Lower the jack and take the bike off the center stand. While sitting on the bike, grab a handful of the front brake and vigorously get the forks pumping up and down maybe 10-15 times. This will allow the fork oil to work down into the lower part of the forks. Now get it back on the center stand and jack up the front end again. Now attach the longer tube and fill up the syringe one more time about halfway. Same thing as above, if it gets caught up, twist the syringe and tubing so all the tubing goes down in. Squirt that in but this time after the syringe is empty, while the tube is still inside, start drawing the plunger out. If fluid starts filling the syringe, you know that it was overfilled and you are now drawing out the excess. empty the excess, put the tube back in and repeat until no more fluid enters the syringe. If nothing comes out then you know you have to add more fluid to that side. Repeat on other side. Pull the tube back out, put the schrader valve back in and you are done. You now have the proper amount of fluid in there. The beauty of this is that it doesn't matter if a little fluid was left behind from draining, the level will never change. If some fluid was left, using the level method, you end up putting in less new fluid automatically anyway. If you were to completely ensure that you drained all the fluid now in the forks, the volume otherwise known as cc's would match the cc's called for in the factory manual.
As a side note, you will now have the proper amount of air in there for Progressive springs. If you check it, even though there is air, it will measure 0 psi. Now when you lower the jacked up front end and take the bike off the center stand, there will be small measurable psi but it actually never changed. The reason this is important is that if you let the air out while the forks are slightly compressed, (normal riding position) it will limit the forks ability to extend all the way if they need to such as rebounding over bumps because you will end up in a negative psi condition with the forks fully extended. Kind of like a vacuum chamber....
Edited to correct the wrong info on the 95+. Thanks again Stan...
I have noticed this topic coming up quite frequently. A search would reveal a lot of different threads and I actually started one a while back myself but I wanted to add a more recent one to help others with this....
This method is works only if there is a schrader/air valve in the top fork bolt.
I have started doing the fork oil change as annual maintenance. There is a method to do it where you can do it very simply and get the level right everytime.
The confusing thing is that level and volume keeps getting interchanged but in essence, they are basically one and the same. If you can figure out the level (distance from the top of the fork tube), then you will already know the volume (amount of cc's) that need to be added. These forks need the level to be equal in both forks even though different amounts of oil go in each. This is because there are different components in the left as opposed to the right and this changes the amounts of oil each one holds. (Although this doesn't apply to Interstate models, they use equal volume in both forks.) But the one constant is that the level will end up being identical. This is because of the level of air needs to be the same in both sides. Even though Progressive says to add no air which technically is correct, there is still air in the forks and this plays into the damping. When the forks are compressed, as in driving down the street, going over bumps, cornering, etc... This amount of air will also play into the mechanics of how the fork works. Because of this, the amount of air needs to be identical in each or there will be different amounts of pressures at work on the left and right forks which could cause a serious handling issue.
An example of volume and level.... Let say you need 1-1/2 cup of milk. You pull out a glass measuring cup and carefully measure it out using the markings. Now you pour that into another glass cup that you plan on using all the time that has no markings. So after you pour the milk into this separate glass, you make a mark at the level where the milk is. The next time you need 1-1/2 cups of milk, you will no longer need to measure it, you just pour the milk into this glass up to the mark and if it goes over, you pour out the excess. If it's too low, just add some more. This will work for everytime you need 1-1/2 cups of milk. Technically you are still measuring out 1-1/2 cups each time but you already know in advance that putting the milk to the mark will get you the amount you need. So no need to think about it.
Satan on this board took the time to do some extensive measuring of the 88-94 and 95-00 forks and simplified the levels. Most times the service manual only gives the levels and volume with springs out and the forks fully collapsed. That is the hard way. Changing the fork oil with the forks fully extended with the springs still in wasn't known and most folks took their best guess at what it should be. But this information is what was wanted. He was in the middle of a fork rebuild so was able to take both measurements and this is what he came up with:
Oil fill with forks collapsed and springs out (from the shop manuals):
239mm / 9.4" for 88-94
194mm / 7.6" for 95-up
Of course that kinda sucks if you've got springs in your bike and you're refilling through the air valve...
... so measuring from the TOP OF THE FORK NUT (schrader valve removed) looks more like this --
Oil fill with forks fully extended and springs installed (measured from the top-plane of the fork nut with the air valve removed):
400mm / 15.75" for 88-94 (Progressive springs installed tight end down)
406mm / ~16" for 88-94 (Progressive springs installed loose end down)
408mm / ~16.1" for 88-94 (OEM springs installed)
* 355mm / ~14" for '95+ (Progressive springs installed tight end down)
* 361mm / ~14.2" for '95+ (Progressive springs installed loose end down)
* 363mm / ~14.3" for '95+ (OEM springs installed)
With that said, the method is foolproof and actually pretty easy way to do it quickly and get the same results each time. All you need is a way to jack up the front of the bike while on center stand so the forks are fully extended, a bottle of your favorite fork oil, a length of aquarium air hose and a syringe like this one:
(Satan used a length IIRC of 3/8" copper tubing straightened and a fender washer to set his level. I use the aquarium tubing because I already had it.) Cut 2 lengths of aquarium tubing. The first one make long enough to reach the bottom of the bottle of fork oil and attach this one first. Second, based on above mentioned levels, figure out which measurement fits your particular application and cut the aquarium tubing to the proper length. If the tubing is too tight, you can use a larger phillips head screwdriver to expand the tubing. It usually has quite a bit of flex before it tears. Obviously drain the old fluid during which removing the schrader/air valve makes it drain quicker. I will sometimes usea nozzleon my compressor set at lowand stick it in the top holeand help blow some of the remaining fluid out. Don't use too high a pressure or fluid will spray everywhere out the drain hole and make a mess. After it finishes draining, put the drain plug back in andstart pulling fork fluid from the bottle through the first aquarium tubing filling the syringe. Now take the end of the aquarium tubing and start putting it through the hole left by the removed schrader valve. Squeeze out the new fluid. Do this about 5 times in each side (based on using a 60cc syringe). Lower the jack and take the bike off the center stand. While sitting on the bike, grab a handful of the front brake and vigorously get the forks pumping up and down maybe 10-15 times. This will allow the fork oil to work down into the lower part of the forks. Now get it back on the center stand and jack up the front end again. Now attach the longer tube and fill up the syringe one more time about halfway. Same thing as above, if it gets caught up, twist the syringe and tubing so all the tubing goes down in. Squirt that in but this time after the syringe is empty, while the tube is still inside, start drawing the plunger out. If fluid starts filling the syringe, you know that it was overfilled and you are now drawing out the excess. empty the excess, put the tube back in and repeat until no more fluid enters the syringe. If nothing comes out then you know you have to add more fluid to that side. Repeat on other side. Pull the tube back out, put the schrader valve back in and you are done. You now have the proper amount of fluid in there. The beauty of this is that it doesn't matter if a little fluid was left behind from draining, the level will never change. If some fluid was left, using the level method, you end up putting in less new fluid automatically anyway. If you were to completely ensure that you drained all the fluid now in the forks, the volume otherwise known as cc's would match the cc's called for in the factory manual.
As a side note, you will now have the proper amount of air in there for Progressive springs. If you check it, even though there is air, it will measure 0 psi. Now when you lower the jacked up front end and take the bike off the center stand, there will be small measurable psi but it actually never changed. The reason this is important is that if you let the air out while the forks are slightly compressed, (normal riding position) it will limit the forks ability to extend all the way if they need to such as rebounding over bumps because you will end up in a negative psi condition with the forks fully extended. Kind of like a vacuum chamber....
Edited to correct the wrong info on the 95+. Thanks again Stan...
damn, and that was gonna be a secret 
